Recording sheets that utilize the color-forming reaction between substantially colorless electron donating dyes (hereinafter referred to as color formers) and electron accepting compounds which develop color upon contact with the color formers (the second group of compounds are hereinafter referred to as developers) include pressure-sensitive copy sheet, heat-sensitive recording sheet, and electrosensitive recording sheet and detailed description thereof are found, e.g., in U.S. Pat. Nos. 2,712,507, 2,730,456, 2,730,457, 3,418,250, 3,432,327, 3,981,821, 3,993,831, 3,996,156, 3,996,405 and 4,000,087.
These recording sheets are available in various forms: in one form, a top sheet comprising a support which is coated with a microcapsule layer containing microencapsulated oil droplets of a color former in an appropriate solvent is placed over a receiving sheet comprising a support which is coated with a layer containing a developer; in a modified case, an intermediate sheet comprises a support one surface of which is coated with a microcapsule layer and the other surface of which is coated with a developer layer; in another form, both the microencapsulated color former and the developer are incorporated in the same surface of a support; in still another form, only one of the microencapsulated color former and the developer is incorporated within the support while the other component is coated on the support.
It has already been proposed that diarylaminofluoran derivatives be used in these recording sheets as color formers that are capable of providing color images having extremely high resistance to light as described in U.S. Pat. Nos. 4,436,920 and 4,390,616. However, the recording sheets containing these diarylaminofluoran derivatives in microcapsules have proved to suffer from the disadvantage that the microcapsule-coated surface turns blue or that any surface of the coating which may be cut is liable to color staining.